This last weekend I built my Digi-Comp I v2.0 which is a replica of a Digi-Comp I which was first released back in 1963.
The Digi-Comp I v2.0 available from Minds-On Toys is made of cardboard verses the plastic of the original. Since originals are hard to come by, this is good alternative. I am still tuning it mechanically but the picture above is basically alternately toggling the A and B flip-flops. It is of course hand operated and the GIF is stop motion without my hand in view :-).
It is great entertainment to researching vintage computing toys and actually being able to own one and build it, to understand it with your own hands is even better.